1. Field of the Invention
The invention relates to a check valve, more particularly to a check valve used in a hydraulic system of a chuck of a machine tool.
2. Description of the Related Art
Referring to FIG. 1, conventional check valves 4, 5 disclosed in Taiwanese Patent Application Publication No. 201130596 are used in a hydraulic system of a chuck of a machine tool. Referring further to FIG. 2, each of the conventional check valves 4, 5 includes a casing 401, 501, a valve member 402, 502 disposed movably in the casing 401, 501, and a resilient member 403, 503 biasing the valve member 402, 502 to block a port 404, 504 defined in the casing 401, 501. By virtue of the conventional check valves 4, 5, the chuck is operable to hold firmly a workpiece (not shown).
Since the casing 401, 501 and the valve member 402, 502 are made of rigid materials (e.g., metal), the valve member 402, 502 may not block the port 404, 504 completely unless they are precisely fitted. However, precision machining of the valve member 402, 502 and the port 404, 504 is costly and time-consuming.